Solenoid

ABSTRACT

A solenoid assembly is provided. The solenoid assembly includes a plunger of magnetic material, the plunger being guided along a rectilinear path from a first end of the path to a second end of the path when a coil surrounding the path is energized. A first member of magnetic material is provided which partially encircles a first part of the circumference of the path near the second end of the path. A second member of magnetic material partially encircles a second part of the circumference of the path near the second end of the path. The extent of circumferential encirclement of the first member and the second member increases in a direction from the first end of the path to the second end of the path.

United States Patent [191 Popovic et al.

[4 1 Jan. 14,1975

SOLENOID Inventors: Djordje R. Popovic, Chicago;

Vahram K. Sarrafian, Glenview, both of Ill.

Assignee: Wico Corporation, Niles, 111.

Filed: May 17, 1974 Appl. No.: 47 1,020

US. Cl. 335/258, 335/281 Int. Cl. Holt 7/08 Field of Search 335/251,255, 258, 281,

References Cited UNITED STATES PATENTS 9/1958 Herion 335/262 11/1965Bennett et al. 335/262 X Primary ExaminerG. Harris Attorney, Agent, orFirmFitch, Even, Tabin & Ludeka [57] ABSTRACT A solenoid assembly isprovided. The solenoid assembly includes a plunger of magnetic material,the plunger being guided along a rectilinear path from a first end ofthe path to a second end of the path when a coil surrounding the path isenergized. A first member of magnetic material is provided whichpartially encircles a first part of the circumference of the path nearthe second end of the path. A second member of magnetic materialpartially encircles a second part of the circumference of the path nearthe second end of the path. The extent of circumferential encirclementof the first member and the second member increases in a direction fromthe first end of the path to the second end of the path.

12 Claims, 8 Drawing Figures PATENTEUJAN 1 W5 3.860.894

FIG. 4

FORCE DIS TA NCE 1 SOLENOID The present invention relates to a solenoidassembly including a solenoid and a plunger. More particularly, thepresent invention is directed to a solenoid assembly whereby theforce-distance characteristics of the solenoid assembly are controlled.

Solenoid assemblies comprising a solenoid and a plunger are well-known.The solenoid assembly includes an elongated tubular magnetic coil whichis adapted to be excited by an external current source, a hollowguidance tube arranged coaxially within the tubular magnetic coil and aplunger of magnetic material arranged slidably in the guidance tube.Usually a spring is associated with the solenoid assembly which tends toguide the plunger outwardly from the end of the guidance tube to a restposition.

When the coil is energized, the plunger becomes magnetized and mutualattraction takes place between the coil and the plunger. The plungerthen moves within the hollow guidance tube until the net opposingmechanical forces balance each other. This occurs when the mutualopposing polarities of the coil and the plunger coincide. The net forceexerted upon the plunger by the opposing mechanical forces is at aminimum at the time just after the coil is energized. The forcegradually increases with the distance moved by the plunger and isusually at a maximum at or near the end of the plunger stroke. Thisforce-distance relationship is represented by curve A of FIG. 5. Becauseof the large force generated at or near the end of the plunger stroke, ahammer blow occurs at the end of the stroke. The hammer blow isundesirable in that it is both noisy and tends to result in prematuresolenoid failure. It would be desirable to control the force-distancecharacteristics which occur during the travel of the plunger within thesolenoid coil. Ideally, the force-distance characteristic would bemodified so that the force is at a maximum shortly after the plungermovement is initiated and levels off or decreases near the end of theplunger stroke. This ideal condition is represented by curve B of FIG.5.

Many devices have been proposed for modifying and controlling theforce-distance characteristics of solenoid assemblies. Toggles, cams,bellcranks and levers have been used in connection with electromagnetsin order to obtain force-distance characteristics different from thoseexhibited by the electromagnet alone. Other methods for altering theforce-distance characteristics involve the shaping and proportioning ofcoils, plungers, armatures, or air gaps. Such known methods formodifying the force-distance characteristics have not been whollysuccessful in that they introduce inherently complicated mechanicalarrangements or involve expensive assembly, machining or shapingoperations during the manufacture of the solenoid assemblies. It wouldbe desirable to provide a simple means for modifying the force-distancecharacteristics of solenoid assemblies and to provide a solenoidassembly with a substantially uniform force throughout the distance oftravel of the plunger.

Accordingly, it is a principal object of the present invention toprovide a solenoid assembly with modified force-distancecharacteristics. It is another object of the present invention toprovide a solenoid assembly which has a substantially uniform forceexerted upon the plunger throughout the distance of travel of theplunger. It is a further object of the present invention to provide asolenoid assembly with modified forcedistance characteristics and yetwhich is simple to manufacture.

Generally, in accordance with various features of the present invention,a solenoid assembly is provided. The solenoid assembly comprises aplunger of magnetic material, the plunger being guided along arectilinear path from a first end of the path to a second end of thepath when a coil surrounding the path is energized. A first member ofmagnetic material is provided which partially encircles a first part ofthe circumference of the path near the second end of the path. A secondmember of magnetic material is also provided and the second memberpartially encircles a second part of the circumference of the path nearthe second end of the path. The extend of circumferentialencirclement ofthe first member and the second member increases in a direction from thefirst end of the path to the second end of the path.

The novel features which are considered to be characteristic of theinvention are set forth below in particular in the appended claims. Theinvention, however, both as to its construction and its method ofoperation together with additional objects and advantages is best s srteqd m h fqt w n sissqrip e of pe embodiments when read in combinationwith the accompanying drawings in which:

FIG. 1 is a view, partially in section of a solenoid assembly inaccordance with an embodiment of the invention;

FIG. 2 is a view, volved 3 w FIG. 3 isa cross-sectional View of thesolenoid assembly of FIGS. 1 and 2 taken along the line 3-3 of FIG.

partially in section, of FIG. 1 re- FIGS. and 4A is a top view and anend view of one of the magnetic members of the invention, prior toshaping the memberj and FIG. 5 is a graph showing various force-distancecharacteristics for various solenoid assemblies.

FIG. 6 isa view, broken away and partially in section, of a solenoidassembly in accordance with an alternate embodiment of the invention;

FIG. 7 is a view, broken away and partially in section of FIG. 6revolved 90.

Referring now to the drawings, a solenoid assembly 11 is shown in FIGS.1 and 2. The solenoid assembly includes a bobbin or guidance tube 13 ofnon-magnetic material having a first flanged end 15 and a second flangedend 17. Arranged coaxially within the guidance tube 13 is a slideableplunger 19. The plunger 19 is provided with a flange 20 at one end. Anelectromagnetic coil 23 is helically wound around the guidance tube 13between the first flanged end 15 and the second flanged end 17. A spring21 is mounted around plunger 19 and urges plunger 19 into a restposition when the coil 23 is unenergized. The coil 23 is adapted to beconnected to a switched external electrical source (not shown) by meansof terminals 24 shown in FIG. 2. As shown in FIGS. 1 and 2 the coil isin an energized state and the plunger 19 is drawn within the guidancetube 13, thus compressing spring 21. An enclosure (not shown) ofmagnetic or other material may be placed around the solenoid assembly inaccordance with the known practice.

A first member 25 of magnetizable material partially encircles guidancetube 13. A second magnetizable member 27 also partially encirclesguidance tube 13. The shape of the first member and the second member issuch that the circumferential encirclement of a first portion of eachmember is constant in a direction along the path of travel of theplunger 19 and the circumferential encirclement of a second portionincreases in a direction corresponding to the path of travel of theplunger 19 when the coil 23 is energized. The first portion of constantcircumferential encirclement of the first member and the second membermay extend a total distance corresponding to from zero to one half ofthe total length of the first member and the second member, the totallength being measured in the direction of travel ofthe plunger 19.

It has been discovered that the presence of the first and secondmagnetizable member alters the forcedistance characteristics of thesolenoid assembly. In this connection, the force-distancecharacteristics of the solenoidassembly with the first and secondmagnetizable member in position are generally as shown by curve C ofFIG. 5. The solenoid assembly of the invention including the firstmagnetizable member and the second magnetizable member is particularlysuitable for improving the force-distance characteristics of a solenoidenergized by a D.C. electrical source so that it resembles an AC.solenoid characteristic. However, improvements in the force-distancecharacteristics of solenoids energized by AC. electrical source may alsobe provided by the solenoid assembly of the invention.

The first and second members are constructed from any suitablemagnetizable material. As best seen in FIG. 4, the member 25 and themember 27 may be constructed from a flat sheet of magnetizable material.The flat sheet is cut into a suitable shape and is then formed into asuitable configuration to encircle the path of the plunger 19, and isplaced around the guidance tube 13 prior to winding the coil 23. a

The first member 25 and the second member 27 may comprise a section orpart of the guidance tube 13.

It is also contemplated that a shape corresponding to the shape ofmembers 25 and 27 can be imprinted upon the guidance tube 13 by use ofmagnetizable ink or by deposition of magnetic particles.

The thickness of the members 25 and 27 is not critical, but the effecton the force-distance characteristics of the solenoid assembly arerelated to the thickness of the magnetized members 25 and 27. In oneembodiment of the invention found to be suitable, the members 25 and 27have a thickness of about 0.048 inches.

The gaps 29 and 30 between the first member 25 and the second member 27are not critical, but the effect on the force-distance characteristicsof the solenoid assembly are related to the extent of the gaps 29 and30. Generally, in one embodiment of the invention found to be suitable,each of the gaps 29 and 30 extends about 7 percent of thecircumferenceof the guidance tube 13.

The rate of increase of circumferential encirclement of the members 25and 27 in the direction of travel of the plunger 19 is not critical.Also, the increase in circumferential encirclement may be uniform, asshown in the drawings, or may be stepwise. However, the effect on theforce-distance characteristics of the solenoid assembly is related tothe rate of increase of the circumferential encirclement and the totaldistance along the path of travel of the plunger over which the increasein circumferential travel occurs. The distance between the second end ofthe path of travel of the plunger 19 and forward terminus of the firstmember 25 or the second member 27 from the first end is preferably atleast one quarter of the total distance of travel of the plunger 19.

As shown in FIG. 2, the first member 25 and the second member 27 areoverlapping in a direction corresponding to the direction of travel ofthe plunger 19. Also, as shown in FIG. 2 the first member 25 and thesecond member 27 are adjacent to and abut the second flanged end 17 ofthe guidance tube 13. Such overlapping and abutting position ispreferred but is not essential for operation for the solenoid assemblyin accordance with the invention to alter the force-distancecharacteristics of the solenoid.

While the invention has been illustrated and described as embodied in aparticular solenoid assembly, it is not intended to be limited to thedetails shown, since various modifications and structural changes may bemade without departing from the spirit of the present invention assetforth in the appended claims.

What is claimed is: t

- l. A solenoid assembly comprising a plunger of magnetic material, saidplunger being guided along a rectilinear path from a first end of saidpath to a second end of said path, a first member of magnetic materialpartially encircling a first part of the circumference of said path atsaid second end of said path and a second member of magnetic materialpartially encircling a second part of the circumference of said path atsaid second end of said path, the circumferential encirclement of saidfirst member and said second member increasing in a direction from saidfirst end of said path to said second end of said path.

2. A solenoid assembly in accordance with claim 1 wherein said firstmember and said second member overlap in a direction along saidrectilinear path.

3. A solenoid assembly in accordance with claim 1 wherein there is a gapbetween said first and said second member.

4. A solenoid assembly in accordance with claim 1 wherein said increaseof said circumferential encirclement of said first member and saidsecond member is uniform.

5. A solenoid assembly in accordance with claim 1 wherein said increaseof said circumferential encirclement of said first member and saidsecond member is stepwise.

6. A solenoid comprising a guidance tube of nonmagnetic material havinga first end and a second end, a plunger. of magnetic material extendingthrough an aperture in said first end and coaxially with said guidmentof said first member and said second member is stepwise.

11. A solenoid in accordance with claim 6 wherein said first endand'said second end of said guidance tube are flanged.

12. A solenoid in accordance with claim 11 wherein said first member andsaid second member abut said flange of said second end.

1. A solenoid assembly comprising a plunger of magnetic material, saidplunger being guided along a rectilinear path from a first end of saidpath to a second end of said path, a first member of magnetic materialpartially encircling a first part of the circumference of said path atsaid second end of said path and a second member of magnetic materialpartially encircling a second part of the circumference of said path atsaid second end of said path, the circumferential encirclement of saidfirst member and said second member increasing in a direction from saidfirst end of said path to said second end of said path.
 2. A solenoidassembly in accordance with claim 1 wherein said first member and saidsecond member overlap in a direction along said rectilinear path.
 3. Asolenoid assembly in accordance with claim 1 wherein there is a gapbetween said first and said second member.
 4. A solenoid assembly inaccordance with claim 1 wherein said increase of said circumferentialencirclement of said first member and said second member is uniform. 5.A solenoid assembly in accordance with claim 1 wherein said increase ofsaid circumferential encirclement of said first member and said secondmember is stepwise.
 6. A solenoid comprising a guidance tube ofnon-magnetic material having a first end and a second end, a plunger ofmagnetic material extending through an aperture in said first end andcoaxially with said guidance tube, a first member of magnetic materialpartially encircling said guidance tube at the second end thereof, and asecond member of magnetic material partially encircling said guidancetube at the second end thereof, the circumferential encirclement of saidfirst member and said second member increasing in a direction from saidfirst end of said path to said second end of said path.
 7. A solenoidassembly in accordance with claim 6 wherein said first member and saidsecond member overlap in a direction along said rectilinear path.
 8. Asolenoid assembly in accordance with claim 6 wherein there is a gapbetween said first and said second member.
 9. A solenoid assembly inaccordance with claim 6 wherein said increase of said circumferentialencirclement of said first member and said second member is uniform. 10.A solenoid assembly in accordance with claim 6 wherein said increase ofsaid circumferential encirclement of said first member and said secondmember is stepwise.
 11. A solenoid in accordance with claim 6 whereinsaid first end and said second end of said guidance tube are flanged.12. A solenoid in accordance with claim 11 wherein said first member andsaid second member abut said flange of said second end.